It is a common situation that a wireless communication device (also referred to as the device hereinafter) supports communication in accordance with two or more radio access technologies (RATs). For example, a mobile telephone may support communication in a wireless communication system using two or more of a RAT in accordance with the GSM (Global System for Mobile communication) standard, a RAT in accordance with the UMTS (Universal Mobile Telecommunication Standard) standard, and a RAT in accordance with the UMTS LTE (UMTS Long Term Evolution) standard.
The subscription identifier (e.g. a subscriber identity module—SIM—card) used in combination with the device may in turn define one or more RATs that are allowed for use in relation to that particular subscription. The RATs allowed by the subscription may be the same RATs as supported by the device. Alternatively, one or more of the RATs supported by the device may not be allowed by the subscription. Yet alternatively (or additionally), the subscription may allow RATs that are not supported by the device. For example, a device that supports GSM, UMTS and UMTS LTE may be used in combination with a SIM card that allows only GSM and UMTS (which is typical for older SIM cards).
In such (and similar) situations, it may be so that emergency calls are allowed over the RAT(s) supported by the device but not otherwise allowed by the subscription. In the example above, emergency calls may typically be allowed over LTE (using VoLTE—Voice over LTE) even though the SIM card allows only GSM and UMTS.
It is, of course, desirable that emergency calls are enabled as far as possible. However, for emergency calls to be possible using a RAT (e.g. UMTS LTE) that is not allowed for normal use by the subscription it is typically required that the device performs various neighboring cell measurements for that RAT also. Such measurements may, for example, include one or more of mobility management (MM) measurements, radio resource management (RRM) measurements, cell search, signal strength measurements (e.g. reference signal received power—RSRP, received signal strength indicator—RSSI, and/or reference signal received quality—RSRQ), etc. Typically, the neighboring cell measurements are then correspondingly processed by the device (including e.g. comparison of signal strength, keeping of a neighboring cell list, etc.).
Performing these measurements and/or the corresponding processing consumes resources of the device such as, for example, power, processing capacity, storage area, etc. It may be desirable to be careful regarding consumption of such resources. For example, high power consumption may require the battery of the device to be charged more often. Furthermore, when the radio of a single radio architecture is used for measurements of one RAT, it cannot be used for measurements and/or communication of another RAT.
Therefore, there is a need for methods and arrangements that enable emergency calls using a RAT that is supported by the device but not allowed for normal use by a subscription used with the device, while keeping related resource consumption of the device at a reasonable level.